In recent years, the demand for secondary batteries as power supplies has been increased with the development of portable devices such as cellular phones and laptop computers. Above all, the development of lithium ion secondary batteries which are high in energy density has been carried out actively.
However, as lithium ion secondary batteries are used for general purposes, the issue of safety against heat generation and ignition of batteries is caused due to an increase in internal energy with an increase in the content of an active material and due to an increase in the content of an organic solvent as a combustible material for use in an electrolyte, and improvements in safety have been required.
Meanwhile, all-solid-state batteries using an inorganic solid electrolyte for an electrolyte have been attracting attention as next-generation secondary batteries. The all-solid-state batteries use, unlike existing lithium-ion secondary batteries and the like, an inorganic solid electrolyte such as incombustible ceramics and glass without using any organic solvent for the electrolyte. Therefore, the all-solid-state batteries have no worries such as ignition or liquid leakage, and have high safety.
Patent Document 1 discloses an all-solid-state lithium-based secondary battery prepared by press molding of a solid-state electrolyte, a positive electrode material, and a negative electrode material. According to Patent Document 1, disclosed is the preparation of a lithium-based secondary battery by filling a predetermined mold with the positive electrode material, the electrolyte, and the negative electrode material and pressing at a molding pressure of 3,700 kg/cm2.
In addition, Patent Document 2 discloses an all-solid-state lithium secondary battery using a carbon material as an electrode active material. According to Patent Document 2, reference is made to the great importance of selecting a lithium ion-conducting solid electrolyte in the case of using graphite as an electrode active material. Disclosed is the fact that, in the case of an all-solid-state lithium secondary battery using a graphite intercalation compound as an electrode active material, the selection of the most preferable electrolyte as an electrolyte to be used allows the all-solid-state lithium secondary battery to have a higher energy density. In addition, disclosed as a preferable electrolyte is a sulfide-based lithium ion-conducting solid electrolyte mainly containing a lithium sulfide and a phosphorus sulfide and containing no transition metal, silicon, or germanium.    Patent Document 1: Japanese Patent No. 3453099    Patent Document 2: Japanese Patent Application Laid-Open No. 2003-68361